The present invention relates generally to magnetometers, and more particularly, to an improved digital fluxgate magnetometer.
The assignee of the present invention designs and manufactures magnetic sensor systems that process data from three-axis fluxgate magnetometer sensors using a variety of magnetic data processing algorithms. Such magnetic data processing algorithms are disclosed in U.S. Pat. No. 5,239,474, entitled "Dipole Moment Detection and Localization", U.S. patent application Ser. No. 08/6111,291, filed Mar. 5, 1996, entitled "Improved Dipole Moment Detector and Localizer", and U.S. patent application Ser. No. 08/611,352, filed Mar. 5, 1996, entitled "Spatial Temporal Processing of Magnetometer Data to Localize Magnetic Dipoles". Present state of the art fluxgate magnetometer sensors use the output of an analog integrator as the magnetometer output. This signal is then digitized with an analog to digital (A/D) converter having a large number of bits of resolution (typically &gt;20). This requires the use of large, expensive, and power hungry analog to digital converters that are presently limited to around 22 bits resolution.
These prior art magnetic sensor systems use an analog magnetic fluxgate sensor, and couple it to a high resolution analog to digital converter to produce a digital output. This approach has a number of disadvantages. The high resolution A/D converters tend to be limited in dynamic range, presently to 22 bits or less. The high resolution A/D converters are expensive. The high resolution A/D converters are physically large. The high resolution A/D converters consume large amounts of power. Furthermore, the analog integrators used in the analog fluxgate sensors cause low level drift in the output signal of the sensor which limits their use in detection and tracking targets.
A stopgap measure presently utilized by the assignee of the present invention to overcome the limitations of the above-described conventional fluxgate magnetometer sensors is to use an adjustable voltage reference and an analog subtractor to subtract (remove) the large constant part of the measured magnetic field due to the earth's magnetic field from the magnetic field measured by the fluxgate magnetometer. Then, the remaining signal is digitized using a reduced resolution analog to digital converter (12 to 16 bits). This technique only works in applications in which the magnetometer sensor is stationary with respect to the earth's magnetic field. Alternative approaches for providing high resolution digitization for fluxgate magnetometer sensors are described in U.S. patent application Ser. No. 08/636,617, filed Apr. 23, 1996, entitled "Digital Flux Gate Magnetometer", and U.S. Pat. No. 5,652,512 entitled "Advanced Digital Flux Gate Magnetometer".
Accordingly, it is an objective of the present invention to provide for a digital fluxgate magnetometer that improves upon the above-described conventional analog magnetometers.